XC Phase weak Phase

Chrisq206

Chrisq206

Member
Built the Pedal. It works, but the phasing seems weak, even after numerous attempts at getting the bias to correct it.


Is there a good place to start troubleshooting?

The signal comes out clear and strong, just seems like the phasing could be stronger. Could that be the nature of the build?

Yes I did get the matched transistors from the place I was supposed to. Can’t remember the name right now though

Cheers
 
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Hi Chrisq206,

I have build my pedal this week - this is my first pedal (was building digital devices only before).
Signal runs through my pedal but I have problems to make it phase as well.

I double-checked:
- values of my components (all brand new ones) - all look OK
- polarity of capacitor and diodes are OK
- all transistors are installed as indicated by the silkscreen
- IC orientation, correct
- I was looking into possible shorts on my PCB (did not find any so far).
Foot switch I used was prewired without info on individual wires - I think I have figured out the wires correctly but I am digging into it again ...

However, I found out that my VREF = ~4.1V only (on Zener 5V1 diode).
Mr. fig (Village Idiot) in one of his post confirms expected VREF is ~5.1V.

So in my case - it looks like I have something that drags my VREF down ...
Chrisq206, could you check your VREF? Is it 5.1V?

Regards,
Peter
 

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peter.vojtenyi said:
Hi Chrisq206,

I have build my pedal this week - this is my first pedal (was building digital devices only before).
Signal runs through my pedal but I have problems to make it phase as well.

I double-checked:
- values of my components (all brand new ones) - all look OK
- polarity of capacitor and diodes are OK
- all transistors are installed as indicated by the silkscreen
- IC orientation, correct
- I was looking into possible shorts on my PCB (did not find any so far).
Foot switch I used was prewired without info on individual wires - I think I have figured out the wires correctly but I am digging into it again ...

However, I found out that my VREF = ~4.1V only (on Zener 5V1 diode).
Mr. fig (Village Idiot) in one of his post confirms expected VREF is ~5.1V.

So in my case - it looks like I have something that drags my VREF down ...
Chrisq206, could you check your VREF? Is it 5.1V?

Regards,
Peter
Click to expand...
Thank you

This is exactly the kind of help I need
 
Upvote 0 Downvote
peter.vojtenyi said:
Hi Chrisq206,

I have build my pedal this week - this is my first pedal (was building digital devices only before).
Signal runs through my pedal but I have problems to make it phase as well.

I double-checked:
- values of my components (all brand new ones) - all look OK
- polarity of capacitor and diodes are OK
- all transistors are installed as indicated by the silkscreen
- IC orientation, correct
- I was looking into possible shorts on my PCB (did not find any so far).
Foot switch I used was prewired without info on individual wires - I think I have figured out the wires correctly but I am digging into it again ...

However, I found out that my VREF = ~4.1V only (on Zener 5V1 diode).
Mr. fig (Village Idiot) in one of his post confirms expected VREF is ~5.1V.

So in my case - it looks like I have something that drags my VREF down ...
Chrisq206, could you check your VREF? Is it 5.1V?

Regards,
Peter
Click to expand...
My VREF was 4.2V at 9v in. Running it at 12v, it would go up to 4.8V. I tested the sound at both VREFS and biased again, because “why not?”

It sounded the about the same at both, maybe 12v was stronger, but not sure

The signal and tone of the pedal are great, but seems like it could phase harder.

I wonder what would bring the voltage down?

I suppose I should compare it to the reissue MXR I have and see

What do you think?
 
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Hi,

Since you have the same VREF I do (I have 4.15V when using 9V power supply), I would assume the circuit is working.
However, it would be nice to get VREF value from somebody whose XC Phase pedal is phasing ..

It might be interesting to compare to MXR Phase if you have one and it has similar power section of the circuit with zener diode.

My pedal might be failing because I have not very well matched 4 x 2n5457 transistors at the moment ...
I have ordered a matched set of 2SK208-GR JFETs and see whether it improves the pedal functionality:
aionfx.com

2SK208-GR, matched set for phasers

This is a matched set of 2SK208-GR JFETs for use in phasers such as the BOSS PH-1r, pre-soldered to adapter boards for through-hole applications.
aionfx.com aionfx.com


Let me know when/if you find out VERF on the MXR - I wonder what the value is ...

Regards,
Peter
 
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Chris,

Just noticed following - the PCB has been created for:
JFET transistors: 2N5952
but I used alternative: 2N5457
.. and when I compare PINs - pin 2 is source on both, but pins 1 and 3 are reversed.

1674096686951.png

I believe (in my case) I need to turn around 4 JFET transistors NOT to match the silkscreen of the PCB.
I need to double-check using original data-sheets and when it is true I will make the change tomorrow and see ...
 
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peter.vojtenyi said:
Chris,

Just noticed following - the PCB has been created for:
JFET transistors: 2N5952
but I used alternative: 2N5457
.. and when I compare PINs - pin 2 is source on both, but pins 1 and 3 are reversed.

View attachment 40508

I believe (in my case) I need to turn around 4 JFET transistors NOT to match the silkscreen of the PCB.
I need to double-check using original data-sheets and when it is true I will make the change tomorrow and see ...
Click to expand...
That’s correct.
 
Upvote 0 Downvote
peter.vojtenyi said:
Chris,

Just noticed following - the PCB has been created for:
JFET transistors: 2N5952
but I used alternative: 2N5457
.. and when I compare PINs - pin 2 is source on both, but pins 1 and 3 are reversed.

View attachment 40508

I believe (in my case) I need to turn around 4 JFET transistors NOT to match the silkscreen of the PCB.
I need to double-check using original data-sheets and when it is true I will make the change tomorrow and see ...
Click to expand...
I used 5952s from the place that’s recommended. I can’t remember the name.

Mine is phasing. I need to check it against the MXR still though
 
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Mcknib said:
You want the FET gates set to about 2 to 2.5v to get you around the sweet spot

Set it via the trimmer with speed fully CCW

Just for reference if I'm unsure of voltages or can't work them out from the schematic I'll check general guitar gadgets version they always include voltages in their instructions

P90 build instructions here

Click to expand...
Compared the XC to my newer MXR. ...e way the old ones were I’ll check the gates
 
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I have fixed orientation of my 2N5457 JFET transistors and leads are connected correctly now.
It looks to me I have hints of phasing now - but since these are my temporary transistors and they are not matched the result is not overwhelming.

I will see how it works when I get matched set of 2SK208-GRs - will be more careful to connect them correctly.

BTW - my VREF is still 4.15V when using 9V power supply.
I wonder whether it is expected/acceptable or should be 5.1V.
 
Upvote 0 Downvote
Mcknib said:
You want the FET gates set to about 2 to 2.5v to get you around the sweet spot

Set it via the trimmer with speed fully CCW

Just for reference if I'm unsure of voltages or can't work them out from the schematic I'll check general guitar gadgets version they always include voltages in their instructions

P90 build instructions here

MXR™ Phase 90™ (Script Logo) | General Guitar Gadgets

www.generalguitargadgets.com www.generalguitargadgets.com
Click to expand...
Mine’s 4.7v on the zener and phases when the 2N5952 gate is at about 1.3v. It doesn’t match the GGG voltages there
 
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